It is well known to produce dichlorohydrins by reacting glycerol with hydrogen chloride (HCl) in the presence of a catalyst. The dichlorohydrins, which are also often referred to as dichloropropanols, are reaction intermediates that can then be used to prepare an epoxide such as epichlorohydrin. Epichlorohydrin, in turn, is a well known compound used for making epoxy resins for various end-use applications.
For example, German Patent No. 197308 teaches a process for preparing a chlorohydrin by the catalytic hydrochlorination of glycerin by means of anhydrous hydrogen chloride. WO 2005/021476 describes a continuous process for preparing the dichloropropanols by hydrochlorination of glycerin and/or monochloropropanediols with gaseous hydrogen chloride with catalysis of a carboxylic acid. WO 2005/054167 also describes a process for producing dichloropropanols from glycerol.
WO 2006/020234 A1 describes a superatmospheric pressure process for conversion of a glycerol or an ester or a mixture thereof to a chlorohydrin, comprising the step of contacting a multihydroxylated-aliphatic hydrocarbon, an ester of a multihydroxylated-aliphatic hydrocarbon, or a mixture thereof with a source of a superatmospheric partial pressure of hydrogen chloride to produce a chlorohydrin, an ester of a chlorohydrin, or a mixture thereof in the presence of an organic acid catalyst without substantially removing water.
FIG. 1 shows an embodiment of the process taught by WO 2006/020234 A1 in which a vessel 36 is fed with a feed stream 31, containing hydrogen chloride; and a recycle stream containing glycerol, glycerol esters, monochlorohydrin and their esters and catalyst, via stream 35. In vessel 36, which may comprise one or more CSTRs (Continuous Stirred Tank Reactors), one or more tubular reactors or combinations thereof, glycerol and monochlorohydrins are converted to dichlorohydins. Stream 32, containing, for example, dichlorohydrins, monochlorohydrins, glycerol and their esters, catalyst, unreacted hydrogen chloride and water exits vessel 36 and is fed to vessel 37. Also fed to vessel 37 is feed stream 33, containing glycerol.
The reaction mixture exiting the dichlorohydrin reactor(s) [reactor vessel 36 in FIG. 1] described in WO 2006/020234 A1, where primarily dichlorohydrin is formed from the reaction of glycerol and monochlorohydrin with HCl, is a mixture of components containing, dichlorohydrins, monochlorohydrins, glycerol and their esters, catalyst, water and unreacted hydrogen chloride as described above. A significant amount of hydrogen chloride (HCl) remains dissolved and unreacted in the reaction mixture because of phase equilibrium between the liquid and the vapor phases in the hydrochlorination reactor(s). The concentration of HCl present in the liquid phase (reaction mixture) can be, for example, in the range of 5-20% by mass, depending on the exact conditions in the reactor such as temperature, pressure and compositions of liquid and vapor phases in the reactor. The HCl present in the reaction effluent, if not used efficiently in the process to the maximum possible extent before forwarding the reaction effluent to a distillation column, will exit the distillation system as a light product. This HCl will exit the top of the distillation column either with the dichlorohydrin product or as uncondensed vapors or both. This HCl is a loss for the process if not recovered and recycled to the process. Additionally, this HCl must be neutralized in a downstream process or in suitable equipment if not recovered and recycled, imposing additional expense to running the process. If this HCl loss is substantial for the process, then the HCl needs to be recovered and recycled to the process to keep the process economical. Recovering and recycling unreacted HCl from the reaction effluent or the distillation column product is very expensive as HCl is wet and, therefore, very corrosive to the equipment required for recovery. Only equipment made of glass lined, Teflon® lined or other suitable plastic lined materials or of exotic metals and alloys such as tantalum, zirconium and Hastelloy™ (trademarked by High Performance Alloys, Inc.) can be used in the process for recovering and recycling HCl, imposing a high cost on the process. Therefore, minimizing HCl in the feed stream to a separation system such as a distillation column without having to recover the HCl is advantageous and overall the least expensive option.
WO 2006/020234 A1, on lines 7-20 of page 26, describes a second vessel where the primary purpose of the second vessel is to convert esters of monochlorohydrins and dichlorohydrins to liberate free monochlorohydrins and dichlorohydrins. See FIG. 1. WO 2006/020234 A1 also states that at least some of the unreacted hydrogen chloride that enters the vessel is also consumed to form mainly monochlorohydrins. WO 2006/020234 A1 further states that the second vessel (vessel 37) may also serve as a means to separate the desired dichlorohydrins from unreacted monochlorohydrins and glycerol and their esters. Vessel 37 may include, for example, one or more distillation columns, flash vessels, extractors, or any other separation equipment; or vessel 37 may be, for example, a combination of a stirred tank, tubular reactor or similar vessel with the aforementioned separation equipment.
WO 2006/020234 A1 neither specifies a process sequence to be followed for the reaction and separation of the desired dichlorohydrins, in the process nor does it distinguish between the type of vessels to be used for the purpose of reacting the effluent of the primarily dichlorohydrin producing reactor(s) with glycerol (or a glycerol-containing stream). WO 2006/020234 A1 does not specify whether the reaction with glycerol is carried out prior to or simultaneously with the separation of dichlorohydrins. The prior known process described in WO 2006/020234 A1 does not specifically use a reactor for the purpose of reacting HCl dissolved in the dichlorohydrin reaction effluent with glycerol for improving HCl utilization in the process and more over, the prior art processes do not use a plug flow reactor for reacting dichlorohydrin reaction effluent with glycerol.
Accordingly, it is desired to provide an improved process with more specific process steps and type of equipment to be used in the process such as using a plug flow reactor for the purpose of reacting HCl dissolved in the dichlorohydrin reaction effluent with glycerol for improving HCl utilization; and it is desired to provide a more efficient, smaller, simpler and a much cheaper reactor for reacting HCl in the dichlorohydrin reaction effluent with glycerol. The present invention is, however, not limited to the production of dichlorohydrins only; it is also useful in the production of monochlorohydrins, for example.
It is also desired to provide a significant reduction in the capital and the operating cost of a glycerol hydrochlorination process which can be integrated into a process for producing epichlorohydrin; and it is desired to provide a more efficient and lower cost process to produce epichlorohydrin from glycerol.